1. Field of the Invention
The present invention relates to a method for controlling a continuously variable transmission having an automatic shift mode for changing the change gear ratio in a stepless manner and a stepped shift mode for changing the change gear ratio manually to a predetermined stepped change gear ratio. Particularly, the invention is concerned with a method which permits a smooth stepped speed change.
2. Description of Background Art
In Japanese Unexamined Patent Publication No. H9-203460 there is disclosed a method for controlling a continuously variable transmission capable of making a shift control with use of a stepped shift mode. According to the method disclosed therein, switching to a stepped shift mode is made by means of a mode change-over switch, and a shift-up or shift-down signal is outputted from a shift switch by operating a shift lever, with the result that a target change gear ratio is selected from among those preset in multi-stages and shift-up or shift-down is performed. Thus, a stepped shift control is made as if it were made by a manual type stepped transmission.
In FIG. 3, the reference mark TH denotes a throttle opening (%), and throttle opening (%) and RC (%) are plotted along the ordinate axis, while time is plotted along the abscissa axis. Separately, vehicle speed is calculated on the basis of a change ratio in the number of pulses per unit time which are fed from the speed sensor 25 constituted by a pulsar.
According to the present invention, for solving the above-mentioned problem, there is provided a method for controlling a continuously variable transmission having an automatic shift mode for changing the change gear ratio in a stepless manner and a stepped shift mode for changing the change gear ratio manually to a predetermined stepped change gear ratio, wherein when it is detected that the deceleration has exceeded a predetermined value while the change gear ratio is changed by a shift-down operation in the stepped shift mode, the change gear ratio changing operation is stopped, and when it is thereafter detected that the deceleration has decreased to a level below the predetermined value, the change gear ratio changing operation which has been stopped is resumed.
Upon shift-down in the stepped shift mode, if the deceleration exceeds a predetermined value during changing of the change gear ratio, a control unit detects this state and stops the change gear ratio changing operation temporarily. By so doing, it is possible to decrease the shift speed and thereby decrease the deceleration to a value smaller than the predetermined value, thus permitting a smooth shift without feeling any shift shock. Thereafter, when it is detected that the deceleration has decreased to a level below the predetermined value, the change gear ratio changing operation which has been stopped is resumed.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.